Catastrophic failure of SG.

[Yoe777]

I came home today to find all of my Transistors blown. Upon investigation I looked at my coil and the core had melted out then grounded on my magnet.

I was approaching 15v on my battery. Does the coil core heat up at this point?


Any ideas on what happened?

[Tom C]

the base of all your transistors stuck wide open it heated the coil to the point it melted everything. current is what heats things up in an electromagnet. or your coil was shorted internally.

Tom C

[Yoe777]

So assuming there was no short, the core of the coil naturally heated up until the glue & plastic melted?

[Tom C]

http://en.wikipedia.org/wiki/Electromagnet

the coil of an SG is an electromagnet

Tom C

[Yoe777]

Yes I know, that's not what I asked though. I have to say that my success using these forums has been minimal and I am starting to loose faith in it.

I love these areas that have been pioneered but I can't be in the same room with the guys that have done it.

That's why I'm here asking specific questions.

[Tom C]

I came home today to find all of my Transistors blown. Upon investigation I looked at my coil and the core had melted out then grounded on my magnet.

I was approaching 15v on my battery. Does the coil core heat up at this point?


Any ideas on what happened?

a coil does not naturally heat up in an SG regardless of the battery voltage. in a proper SG the coil is not on long enough for the coil to saturate and create heat. that is the answer to your question. the coil is an electromagnet and when it is oversaturated with current it "naturally" heats up. so your transistor stuck on (it stopped switching) which causes current to flow continuously thru the coil.

hope that helps.

Tom C

[Yoe777]

Got it. I only had the SG running 3 days. Did I just get a bad transistor? Also where would I place a fuse in the board to prevent a similar issue again?

[BobZilla]

Yoe,

How about a picture or two of the machine? It might help if we could at least see what you are asking us to diagnose.

Obviously a bad transistor could happen but I think it is more likely you have something configured to cause it to happen.

Are you using ceramic magnets? How far apart is the spacing? The reason I ask these questions is because it is the induction from your magnets on the trigger winding which activates the current through your power winding. If you have the magnets too close you will basically have the base activated without OFF periods. If you used the wrong magnets you could be inducing too strong of a current on the trigger. What about your base resistance, how much did you use and what size/length is your trigger?

[Yoe777]

3" spacing, the magnets are the recommended ones in the SG Handbook, 1"x2.5" Ceramic #8.

[Yoe777]

Additional pics.

[min2oly]

My guess is the same as Tom's,
however, slightly different tangent. One transistor or more is stuck ON. Perhaps a bad solder joint. I've been doing this for a while and had some bad solder joints of my own I had to re-do when I put that board together. A bad solder joint could remove the path the spike has to take to the charge battery and instead melt, pop, burn your transistor leaving it in the on position.
If you connect your charge battery back up with a good coil in place (no trigger)... then touch the run battery momentarily or so..., see which transistor is getting hot. You can then swap it out/remove it, if it's only one, run your experiments off of 7...
hope this helps. Double check all your solder joints after you remove the bad one. In fact, once you find the hot transistor, check the joints before you remove it.
Kind Regards,
Patrick

Got it. I only had the SG running 3 days. Did I just get a bad transistor? Also where would I place a fuse in the board to prevent a similar issue again?

[BobZilla]

Your magnets look good so forget what I was saying about that possibility.

I agree with Patricks idea, if you have a shorted tranny what he suggested will help you find it.

Also I just remembered a long time ago when I had one of my power windings reversed I cooked a tranny, you may want to check that all of the tops are really tops and bottoms are bottoms. That machine ran for awhile without my noticing the mistake and it was the heat that eventually led me to figure out what I had done. It is easy to get one switched around.